srowen commented on a change in pull request #25287:
[SPARK-28552][SQL]Identification of different dialects insensitive to case by
JDBC URL prefix
URL: https://github.com/apache/spark/pull/25287#discussion_r339561571
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File path: sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala
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@@ -56,13 +57,26 @@ case class JdbcType(databaseTypeDefinition : String,
jdbcNullType : Int)
*/
@DeveloperApi
abstract class JdbcDialect extends Serializable {
+ /**
+ * The tag of the database, it must be lowercase, the subsequent will match
+ * the corresponding dialect through this tag, so it must be strictly
one-to-one
+ * correspondence with jdbc url,such as:
+ * mysql url: jdbc:mysql://localhost/db dbTag: mysql
+ * oracle url: jdbc:oracle://localhost/db dbTag: oracle
+ * db2 url: jdbc:db2://localhost/db dbTag: db2
+ * ......
+ */
+ def dbTag: String
Review comment:
Hm, the problem here is that this will break any custom dialects as it adds
a new required method to implement. I am not sure it's worth it, even though we
can possibly introduce such breaking changes. Part of the reason I don't think
it's worth it is just that a non-lowercase string is pretty nonstandard.
I would either push the lowercase down into each implementation, or provide
a default implementation that returns nothing. That at least covers existing
implementations which will already override `canHandle`.
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